Furnace



2 Sheets-Sheet l FURNACE I nvenibr Pe we zivaZB. GrooZaer 55%; @44 I s P. B. CROCKER Filed July 50, 1931 June 12, 1934.

June 12, 1934. P. B. CROCKER FURNACE Filed July 30, 1931 2 Sheets-Sheet 2 I nve fife? P07 0152) aZBL 0W0 ckezz Z (96 7 M fl vf 2 :11; 8

Patented June 12, 1934 1,962,482

UNITED STATES PATENT OFFICE FURNACE Percival B. Crocker, Taunton, Mass, assignor to The Sentry Company, Taunton, Mass, a corporation of Massachusetts Application July 30, 1931, Serial N0. 554,023

Claims. (Cl. 219-36) This invention relates to furnaces and in its be bevelled off toward the side of the projecting E more specific aspects to electric tube furnaces, portions 23 and 25, giving them a substantially particularly those designed to operate at high frusto-pyramidal form and permitting the insutemperatures for combustion analysis and similating material 33 to extend partly over the ends 5 lar work. The object of the invention is to of the chamber which thus retains the heat .60 provide improvements in the construction of better.

furnaces having various advantages in manu- As seen from Fig. 4, the end elements 9 and facture and use, as will appear from the follow- 11 are provided at the location of the projections ing description. 23 and 25 with suitable openings, herein a cen- My invention will be well understood by refertral opening and two lateral openings, provid- ,65

ence to the following description of an illustraing respectively for the reception of the mufiie tive embodiment thereof shown by way of tube 35 and the heating elements 37, which example in the accompanying drawings, latter preferably take the form of resistor bars wherein:- of silicon carbide. Referring to Fig. 3, the open Fig. 1 is a perspective view of the furnace; ings 39 through the end elements 9 and 11 which .70

Fig. 2 is a central longitudinal section on a receive the resistor bars are preferably chamlarger scale with part broken away; fered interiorly as shown to reflect heat gen- Fig. 3 is a longitudinal section on one side of erated in the ends of the heating elements back the center through one of the resistance to the furnace chamber and also to facilitate elements; placing and centering of the bars, and the bars 75 Fig. 4 is a transverse section looking toward 37 extend in these openings through the greater the front of the furnace; and portion of the thickness of the end wall to Fig. 5 is a section through one of the elements adjacent the outer boundary thereof. As seen which forms a heating chamber taken on the at the left of the figure, one end of bar 37 is line 55 of Fig. 4. supported by a terminal 41, the end of which .80

The furnace whichI am about to describe may enters for a short distance in the opening 39 be briefly characterized as comprising a heating and the outer end of which abuts against a chamber suitably insulated exteriorly in which plate of I10n-00nd11 t material 43 Supported is disposed a muilie for the work to be heated in spaced relation from the front of the furand heating elements disposed in the chamber nace by studs 45 and 47. A similar terminal 85 adjacent to the mufile. 49 slightly entering opening 39 in the rear end Referring to Figs. 2 and 3 of the drawings, .member 11 engages the rear end of resistor bar the heating chamber may comprise front and 37 and a Sp 1 C e y a 3 t rear end elements 9 and 11 of fire-brick or the rear of the furnace presses against this similar refractory material which may be proterminal and cOmpressing e p t a ainst the .90 vided (see Figs. 4 and 5) with lower flanges 13 abutment 43 retains the resistor bar in posiand lateral flanges 15 for the support of the tion. An electric connection at 55 supplies curbottom slab 1'7 and side slabs 19 of refractory rent to on of the resistor bars and the current material, the latter supporting the top slab 21, may p s through the r nn ction 57 a and these four slabs in cooperation with the the front of the furnace behind thefihield 43 5 end elements 9 and -11 forming th heating .to the resistor bar at the other side and goes to chamber. The elements 9 and 11' are provided th other Side Of the n through C ect on respectively with the projections 23 and 25 on similar to at the rear of the furnace. In the their exterior faces which are received in openrr n wn the he in lement comes 1' 45 ings in the frame-like end plates 27 which may sufliciently far to the outside of the furnace so .100

be connected by bolts 29 (Fig. 1) holding the that the end is somewhat cooled and danger of various parts in assembled relation. The end corroding the terminals is lessened. At the same plates 27 may be formed with legs 30 supporting time the terminals 41 and 49 do not extend the furnace chamber in a convenient elevated sufficiently far into the heating chamber to be '50 horizontal position. Interposed between the end corroded. To provide for cooling the terminals,

plates 27 is a light metal casing 31 serving to their exteriorly exposed surfaces are preferably retain heat insulating material 33 about the provided with heat-radiating fins as shown.

heating chamber. An important feature of my invention is the It will be seen by comparison of Figs. 2 and 3 form of muflle tube 35. This comprises a main '55 that the sides of the end elements 9 and 11 may cylindrical body 59 which may pass through an opening in front of the end element 9 and through opening in plate 43, as best shown in Fig. 2. It will be understood that the material to be heated may be inserted in the mufile through the open end of the tube which is exposed at the front. The rear end of the tube, however, is preferably reduced in diameter before it passes through the rear wall 11. Herein the tube is provided with the reduced cylindrical portion 61 of considerably less length than the thickness of the rear wall providing a supporting bearing for the tube in that wall and defining with the main body of the tube a shoulder 63 which herein is received in the chamfered portion 65 of the central opening tov the said rear wall. The end of the tube is again reduced within the distance represented by the thickness of the rear wall of the furnace, there being herein shown a conical portion 67 merging with the cylindrical portion 69 which extends out at the rear of the furnace, the'projectingend providing for the connection of a rubber tube thereto to receive gaseous products from the muffle, as is customary, for instance, in the practice of combustion analysis.

When the muffle tube is constructed in this manner there is a marked reduction in the heat emitted from the furnace. This savingin heat givesbetter furnace economy as the chamber requires less heat energy, reducing the amount of energy which must be supplied to the furnace and thus reducing the cost of operation. The saving in heat lowers the temperature at the extreme end of the tube,'reducing the danger of burning the rubber connection tube, and permits the connection of the latter tube to be made in'close proximity to the furnace. This in turn, by minimizing the necessarylength ofprojecting tube, reduces the danger of breakage.

The saving of heat is in conduction, convection and radiation. With respect to loss of heat by conduction, this is, of course, in proportion to the cross section of the conducting material, and as the reduction in diameter of the annular section of the tube reduces the area proportionally to the square of the radius, the restricted tube has much less material in its wall to conduct heat. Less heat is lost by convection currents as the tube is small and air currents are not so free to circulate about inside the tube and carry heat from the heated interior section to the cool exterior portion. Less heat is lost by radiation. Radiant heat travels in straight lines, as does light. The interior surface of the shoulder 63 at the interior of the furnace will stop practically all of the radiant heat and prevent its falling on the unheated outside section.

I am aware that the invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and I therefore desire the present embodiment to be considered in all respects as illustrative and not restrictive; reference being had to the appended claims rather than to the foregoing description to indicate the scope of the invention.

I claim:

1. A furnace of the class described comprising refractory end elements having exterior projections, refractory means between said end elements cooperating therewith to define a chamber, end plates having openings receiving said projections, means connecting the end plates to hold the parts assembled, said end elements having suitable openings at the location of said projections providing for introduction of Work to the chamber and for connection to heating elements therein.

24A furnace of the class described comprising refractory end elements having exterior projections and interior flanges, refractory slabs positioned by said flanges to define in cooperation with said elements a chamber, end plates having openings receiving said projections, means connecting the end plates to hold the parts assembled, said end elements having suitable openings at the location of said projections providing for introduction of work to the'chamber and for connection to heating elements therein.

3. A furnace of the class described comprising refractory end elements of substantially frustopyramidal form and having projections at their smaller bases, refractory means between said end elements cooperating therewith to define a chamber, end plates having openings receiving said projections, insulating material surrounding said chamber between the end plates, means connecting the end plates to hold the parts assembled, said end elements having suitable openings at the location of said projections providing for introduction of work to the chamber and for connection to heating elements therein.

4. A furnace of the class described comprising refractory end elements of substantially frustopyramidal form having flanges at their larger bases, refractory slabs positioned by said flanges to define in cooperation with said elements a chamber, end plates engaging said elements at their smaller bases, insulating material surrounding said chamber between said end plates, means connecting said end plates to hold the parts assembled, said end elements having suitable openings providing for introduction of work to the chamber and for connection to heating elements therein.

5. An electric furnace having openings in opposed walls thereof, one of said openings being internally chamfered, and a muffle tube having a cylindrical body extending through an opening, said body being reduced to provide a shoulder entering the chamfered portion of the other opening and a reduced extension projecting out through the wall.

PERCIVAL B. CROCKER. 

